Bret Devereaux

and even then, the states arguably wasn't a "consolidated democracy" until the civil rights movement of the 60s

which just gets to the inherent difficulty here of defining terms in a consistent way across literal millennia of social change athens was a "democracy" in the most literal sense, but does that mean that their system is "the same" as ours?

Obviously there are differences, but that further undermines the idea of a general rule. That said, I'd think a polis democracy with a few thousand, mostly homogeneous voting citizens ought to be harder to deconsolidate than a diverse country of 300m citizens!